1. Field of the Invention
The present invention relates to a package for electronic components and especially hybrid components. The invention is more particularly applicable to packages which are subjected to airtightness tests after closing of the package by a lid.
2. Description of the Prior Art
In applications such as the aerospace field which require particularly reliable packages from the point of view of airtightness, the packages are tested over a period of two to three months in order to check their stability of airtightness in time.
As a rule, a package is tested at the time of closing by introducing a mixture of nitrogen and a predetermined dose of helium into the package just before fitting the lid and by immediately detecting helium leakages from the package. A test of this type can be performed only instantaneously at the time of closing of the package since, in the event of leakage, the helium disappears almost immediately.
In order to subject a closed package to an airtightness test, it is a customary practice to adopt a method known as "sweating" which consists in putting the package under a pressure of the order of 2 to 4 bar so as to inject helium into the package through any leak locations which may exist. The next step consists in detecting the presence of helium which emerges from the package and thus indicates that leakage is present. In the event that the package is leak-tight, the helium will not have been able to penetrate into the package at the time of injection and no outleakage of helium will consequently be detected.
The problem of testing by the "sweating" method is that pressurization of the package has the effect of forming cracks in the glass beads through which the connecting-leads pass from the interior of the package to the exterior. A cracked package which does not exhibit any leakage at the time of airtightness tests in accordance with the sweating method is not reliable for all that since it is weakened and consequently presents a considerable danger of deficient airtightness in the short term.
Fissures or cracks in the glass beads are due in particular to the bending stress to which lateral walls of the package are subjected by reason of the pressure forces applied on the top face of the lid at the time of putting under pressure. The fact that a soldering process is adopted in order to close the lid on the package and that the soldered joint between the lid and the top face of the walls is concentrated towards the exterior of the package has the effect of increasing the bending phenomenon even further.
It is thus usually observed that the cracked beads located in the central portions of the lateral walls are greater in number than the cracked beads located at the sides close to the point of junction with a lateral wall which extends in another direction. This is explained by the greater rigidity of the lateral walls in proximity to the corners of the package.
A first solution which has already been proposed consists in increasing the rigidity of the lateral walls in the portion located between the glass beads and the lid by widening the walls so as to limit the deformations of the lateral walls when the package is put under pressure.
This solution is practically ineffective since the glass or ceramic beads are too sensitive and the intervals of material which remain in the longitudinal direction between the beads in the lateral walls are usually too small to ensure that the beads are not subjected to any stress.
The aim of the present invention is to remove the disadvantages described in the foregoing by constructing a package for electronic components and especially hybrid components to which airtightness tests can be applied in accordance with the so-called sweating method without any danger of impairment of airtightness of the package as a result of the tests themselves.